Many electronic systems use multiple voltage levels in the same system, and often in the same component. Electronic systems use various voltage levels to drive signals and promote particular operating characteristics for a circuit. For example, a memory chip may require several different voltage levels to operate, such as a main supply voltage, a main supply ground, a bulk voltage, and a negative word line voltage.
Many power supply schemes have been developed for accommodating the different voltage levels. One possible configuration is to minimize the number of voltage levels by using identical voltage levels for different functions. For example, a memory may be configured to use the same voltage level for the bulk voltage VBB and the negative word voltage VNEG. Using identical voltage levels for different signals, however, reduces flexibility and tends to inhibit optimal operation.
An alternative solution is to provide a dedicated circuit including a charge pump for each voltage level to provide the requisite power to the system. These systems are relatively expensive, however, for each dedicated circuit in the system requires additional materials, fabrication, testing, chip space, and design. Further, using dedicated circuits for each voltage level adds complexity. For example, the various voltage level supply circuits may require activation in a selected sequence to avoid latchup problems.